swap: make each swap partition have one address_space
When I use several fast SSD to do swap, swapper_space.tree_lock is
heavily contended. This makes each swap partition have one
address_space to reduce the lock contention. There is an array of
address_space for swap. The swap entry type is the index to the array.
In my test with 3 SSD, this increases the swapout throughput 20%.
[akpm@linux-foundation.org: revert unneeded change to __add_to_swap_cache]
Signed-off-by: Shaohua Li <shli@fusionio.com>
Cc: Hugh Dickins <hughd@google.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/util.c b/mm/util.c
index 16a73195..ab1424d 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -6,6 +6,7 @@
#include <linux/sched.h>
#include <linux/security.h>
#include <linux/swap.h>
+#include <linux/swapops.h>
#include <asm/uaccess.h>
#include "internal.h"
@@ -389,9 +390,12 @@
VM_BUG_ON(PageSlab(page));
#ifdef CONFIG_SWAP
- if (unlikely(PageSwapCache(page)))
- mapping = &swapper_space;
- else
+ if (unlikely(PageSwapCache(page))) {
+ swp_entry_t entry;
+
+ entry.val = page_private(page);
+ mapping = swap_address_space(entry);
+ } else
#endif
if ((unsigned long)mapping & PAGE_MAPPING_ANON)
mapping = NULL;